I agree. There are probably countless ways we could have left. Trump planned for us to leave Afghanistan months sooner than this even and if you think his plan would've stopped their president Ashraf Ghani from immediately fleeing the country the way he did, I think you're playing yourself.
Anyways what I'm basically saying is if we bring (all) the troops home from Afghanistan, no matter what method, how slowly we do it, how quickly we do it, or how much more money we spend doing it, the most sav mofos in Afghanistan will take over the country. After we leave, they take over. It's as simple as that.
South Korea is a totally different situation. How many any US troops been killed there? I mean even going back 60 years.. There is little direct risk to us being there and an obvious reason to be there. Also if we did leave S. Korea and Kim Jong Un attacked them, I seriously doubt their government would just immediately let them take over the way Afghanistan did... Just saying.